University of

1
Solar Car Battery Management System and Solar
Array
University of Pennsylvania Department of
Electrical and Systems Engineering ABSTRACT
Solar racing has increased in popularity over
the past few years due to the greater frequency
of solar competitions. Most competitions are
designed to be fun and promote awareness of
alternative energy and new technologies. The
North American Solar Challenge is a cross-country
race, starting from Austin, Texas and ending in
Calgary, Canada specifically aimed at college
level competition. Penn Solar Racing is
creating a new car to enter in the 2005 North
American Solar Challenge. In order to race, each
solar powered vehicle stores energy from solar
cells in a battery pack and uses this energy to
power a motor. This project will allow Penn
Solar Racing to effectively compete against other
teams in the North American Solar Challenge while
minimizing cost. Minimizing cost will be
accomplished by selecting appropriate batteries
and solar cells and designing a battery
protection system and solar array to be
constructed by students. AUTHORS Michael
Ashley EE 05 Zhenming Zhang EE
05 ADVISOR Professor Jay Zemel DEMO
TIMES Thursday, April 21st, 2005 930AM, 10AM,
1030AM and 1130 AM GROUP 7
Batteries Thirteen lithium polymer batteries from
Electrovaya were chosen for the solar
car. Battery Protection System The battery
protection system monitors the batteries used by
the solar car for overvoltage, undervoltage,
overtemperature and overcurrent conditions. The
battery protection system is made of 13
differential amplifiers and two PIC
microcontrollers, one to monitor battery voltages
and current and another to monitor battery
temperatures. If the battery conditions exceed
desired values, the PICs disconnect the batteries
from the electrical systems of the solar car.
Overvoltage and Undervoltage Protection The
voltage from the differential amplifiers is sent
to a PIC 16F777 Microcontroller. The analog
voltage of the batteries is converted to a
digital value using 13 A/D converters in the
PIC. Overtemperature Protection The batteries
contain built in temperature sensors. The analog
voltage from the temperature sensors is converted
to a digital value using 13 A/D converters in the
PIC. Overcurrent Protection A Hall Effect
current sensor measures how much current is
passing through the batteries. A 50 Amp fuse
will also be used for overcurrent
protection. Solar Array Five Hundred
polycrystalline silicon solar cells were donated
by Mitsubishi Electric to comprise the solar
array. Solar Array The solar array is divided
into five sections. Each section contains
several smaller modules which allow cells to be
wired together and placed on the car. Modules
are of similar size and can be replaced during
the race with spare modules if cells on the car
are damaged.
Battery and Temperature Protection System PCB
Design
Differential Amplifier PCB Design
Battery and Temperature Protection System PCB
Board
Differential Amplifier PCB Board
Solar Array Module Layout